Novel epigallocatechin gallate-based polyether surfactants: Synthesis, characterization and demulsification properties

Natural polyphenols such as tannins, procyanidins, and cardanol are widely used in the field of surface chemistry. To further explore the application of the other natural polyphenols, epigallocatechin gallate (EGCG) derived from green tea was employed. EGCG is an ideal choice to achieve a hyperbranched surfactant. A precursor (EGA) was first obtained by the reaction among the EGCG, formaldehyde, and tetraethylenepentamine (TEPA). EGA surfactants were synthesized in the high-pressure kettle by anionic polymerization with EGA, propylene oxide (PO) and ethylene oxide (EO). The good consistency between the designed PO/EO ratios of EGA surfactants and the theoretical values were proved by 1H NMR spectra. The increase of micelle size with the increase of surfactant concentration and NaCl concentration was observed both by dynamic light scattering and TEM. Result shows EGA surfactants with higher absolute value of increment G-ads and high interfacial activity have potential demulsification applications. As a result, toward aging oil emulsions of the South China Sea Oilfield, the surfactants exhibited excellent demulsification performance. The dehydration ratio reached 94.3% at a low concentration of 100 mg L-1 for 100 min at 70 degrees C, while the commercial demulsifier SP169 only reached 86.9%. This emulsion could be dehydrated completely at even higher temperature at 80 degrees C as well as higher dosage in 150 mg L-1. Meanwhile, the demulsification ratios of crude oil emulsions and aging oil emulsions produced from Bohai Oilfield reached 94.0% and 95.0%, respectively. Coming from the waste oil after demulsification, aging oil emulsions have more additives than crude oil emulsions, therefore the former is more stable. In addition to the above high interfacial activity, this excellent demulsification performance may result from the assistance of polyphenol structure and multiple branches of EGA surfactants. The demulsification of three above emulsions demonstrated that although there exist great differences in properties of emulsions, EGA surfactants exhibit the universality of efficient demulsification.